1. Field of the Invention
The present invention relates to an apparatus and method for controlling a motor. More particularly, the invention relates to an apparatus and method for compensating false speed errors repeatedly generated by a direct current (DC) motor.
This application claims the benefit of Korean Patent Application No. 10-2006-0002677, filed on Jan. 10, 2006, the subject matter of which is hereby incorporated by reference.
2. Description of the Related Art
Hard disk drives (HDDs) are commonly used within various host devices, such as personal computers (PCs), as data storage devices. In general operation, HDDs allow data to be written to and read from recording medium (e.g., a disk having a surface subject to variation in its magnetic properties) using a magnetic read/write head. Data is stored on conventional disks in terms of bits per inch (BPI)—a recording density defined in relation to the disk's rotational direction, and tracks per inch (TPI)—a recording density defined in relation to the disk's radial direction. Significant research and development efforts are currently being expended to increase data recording density according to both of these definitions. Additionally, commercial demands are increasing for increasingly small HDDs. The increasing miniaturization of HDDs, together with demands for higher data recording densities, require ever finer and more precise mechanisms within HDD structures.
Conventional HDDs typically rotate one or more disks at a constant angular velocity using a brushless direct current (DC) motor. A feedback signal having a defined sampling frequency is commonly used to control the rotational speed of the disk. Thus, increased precision over the rotational speed of the disk may be obtained by increasingly the sampling frequency rate.
In contemporary HDDs, the rotational speed imparted to the disk by the spindle motor is estimated and controlled in relation to a back electromotive force generated by the motor. This approach provides excellent control while reducing production costs because a separate sensor adapted to detect the motor's rotational speed in not required.
Speed estimation for the motor is typically performed by applying a phase-defined signal as a driving circuit of the motor. The phase signal may be readily generated whenever the back electromotive force generated by the motor passes a zero point, thereby changing the phase of a corresponding back electromotive force. Thus, the phase of the back electromagnetic force changes in relation to the number of magnetic poles in the motor during the rotation of the disk. Therefore, if the motor is controlled by being synchronized with such phase changes, the sampling rate should correspond to the maximum number of magnetic poles apparent in the operation of the motor.
However, if the sampling frequency is increased, the resulting changes in the interval of magnetic poles due to the mechanical tolerance of a permanent magnet within the motor will negatively affect the system's performance. This causes false errors when the measured speed is used as a feedback signal to an HDD controller, and thus, resonance may be generated in the spindle motor.